The Preparation Of Silver Nanomaterials For Flexible Printed Electronics

With the development of electronic devices and related applications,more and more attentions have been drawn to printed electronics,which is still on the way of being intelligent,integrated,thin and light.Flexible printed electronics are based on the preparation of the flexible/stretchable devices by printing process with low cost,simple manufacture and designable.By combining the conductive inks with the printing technology,a green,additive and high-speed manufacture can be achieved.Two kinds of conductive film were required in flexible electronics.The one is the conductive pattern,which is usually fabricated by etching the metal foils,large amount of waste liquid polute the environment.The other one is the large-area conductive film,which is usually prepared by a sputtering process with inorganic oxide,such as indium doped tin oxide?ITO?,but the cost and resource problem have to be considered.Silver has a lot of potential in flexible electronics for the perfect electrical conductivity and stability.Unfortunately,electronic inks based on silver have not realized industrial application for the high cost and quality problems.Therefore,silver-based conductive materials need to be further studied.In this thesis,the preparation and application of silver-based conductive materials in styles of non-particle conductive ink,silver nanoparticles,and silver nanowires were focused.A mass production process was developed with the synthesis parameters optimized and mechanism researched.Moreover,the flexible applications in electronic devices were also explored.Shortly,the main research works and innovations can be summarized as the followings:1.2-amino-2-methyl-1-propanol?AMP?was firstly used for the synthesis of conductive ink,with silver carbonate served as a precursor,which dissolved in AMP/methanol,non-particle silver conductive ink was synthesized in a rapid way.The film obtained at the ratio of AMP to methanol is 1:1.5 showed more compact with the best conductivity.Typically,the silver content of the non-particle silver conductive ink was 13.2 wt.%and the sintering temperature was lowered as 100oC.The specific resistance was 5??·cm,which is about 3 times of that of the bulk silver.The lone pair electron on amino of AMP can be effectively be complexed with the silver ion in the silver carbonate,thus reducing the redox potential,which is critical to the decomposition temperature.At the same time,the complexation accelerated the solubility of silver carbonate precursor and promoted the silver content of the conductive ink.2.Silver nanoparticles with size less than 20 nm were prepared on a large scale by a microwave-assisted method at a large parameter range.In order to realize fast sintering,a SiO₂ based coating was studied,which was well matched with the silver nanoparticles ink.Once the line was written on the coating by the conductive pen,a good conductivity achieved by chemical sintering in several minutes without any further treatment.Besides,the transmittance of the coating on PET can reach 68%,which enabled its application as a transparent or translucent substrate for conductive circuit printing.3.Silver nanowires?Ag NWs?with a diameter of 30⁵0 nm and length of 30⁶0?m were prepared by modified polyol method with compound alcohol solutions.With the increasing of drop speed of silver nitride,the diameter became smaller along with the increase of the silver nanoparticles,and the optimum interval drop speed was 10¹5rpm;With the increase of KBr,the Ag NWs became thinner and the length can reach60?m with a slenderness ratio of 1000.The optimum synthesis temperature was set at130¹40oC,at which the reaction time was shortened and the yield of Ag NWs was maximized.PVP with different molecular weights can adjust the ratio of length to diameter.The pure Ag NW TCFs have good transparency and conductivity,also with an outstanding mechanical stability,which can resist 5000 bending cycles without an obvious change in conductivity.Hot-roll pressing and Poly?diallyldimethylammonium chloride??PDAC?improved the properties by decreasing the contact resistance.4.In order to improve the properties of transparent conductive film?TCF?,two methods were provided.On the one hand,hydroxypropyl methylcellulose?HPMC?was utalized for dispersing the Ag NWs;On the other hand,graphene oxide?GO?and single-wall carbon nanotubes?SWCNT?was used to fabricate hybird TCF,respectively.The Ag NW/HPMC TCF was applied for the heaters,liquid crystal dimming device,and electrochromic device.HPMC/Ag NW showed an excellent potential in the heater with thermal efficiency of 417oC/?W/cm²?,and the attempt for the flexible liquid crystal dimming device and electrochromic device proved the feasibility in replacement of ITO in future.And the interaction between GO and Ag NWs can decrease the resistance and improve the transmittance,owing to the electrostatic interaction and compaction of GO by solvent evaporation,and ascorbic acid treatment can further improve the properties by forming hererojunction.The maximum current that the heater based on Ag NW/SWCNT can resist was as high as 4 A.The reason can be attributed to the SWCNTs can act as bridges to transport the electrons and decrease the contact resistance,which is beneficial to the uniform distribution of heat and avoid the failure cursed by local overheating.